docs: def dchans(self, key=None):
          """ Return the dchans updated with indch
  
          Return a dict with all keys if key=None
  
          """
          if self._dtreat['indch'] is None or np.all(self._dtreat['indch']):
              dch = dict(self._dchans) if key is None else self._dchans[key]
          else:
              dch = {}
              lk = self._dchans.keys() if key is None else [key]
              for kk in lk:
                  if self._dchans[kk].ndim==1:
                      dch[kk] = self._dchans[kk][self._dtreat['indch']]
                  elif self._dchans[kk].ndim==2:
                      dch[kk] = self._dchans[kk][:,self._dtreat['indch']]
                  else:
                      msg = "Don't know how to treat self._dchans[%s]:"%kk
                      msg += "\n  shape = %s"%(kk,str(self._dchans[kk].shape))
                      warnings.warn(msg)
              if key is not None:
                  dch = dch[key]
          return dch